The aerodynamic airflow around a wing with a finite wingspan results in the formation of a three-dimensional flow pattern, in which streamlines are diverted in the direction of the fuselage, i.e., to the inside, on an upper side of the wing, and to the outside, toward the wing tip, on a lower side of the wing. The scope of this effect depends on how the circulation is distributed over the wingspan. In local wingspan sections, such a gradient in this circulatory distribution results in the formation of a so-called free vortex in the wake of the airfoil in the depth direction. In general, how the circulation is distributed over the wingspan is oriented to the optimum elliptical lift distribution leading to the lowest induced drag. As a consequence, the gradient of circulation over the wingspan increases toward the wing tips, with streamline diversion and free vortex formation being greatest there according to the lifting line theory, which in turn affect the flow pattern and provide a streamline diversion. However, the pressure compensation at the wing tips in the end causes the three-dimensional flow pattern to be most pronounced there, even given other types of circulation distribution.
In order to mitigate this effect and thereby reduce the induced drag of the aircraft, specially formed wing ends (also called “winglets”) are arranged on the wing tips. The winglets essentially help reduce flow around the wing tips, and their suitable shape generates a thrust component.
In addition to relatively classic commercial aircraft with clearly separated fuselage and wings, there also exists the concept of a specific flying-wing aircraft, also referred to as “blended wing body”, abbreviated BWB. A fuselage and wings there form a continuous and harmonious shape, which together generate the lift required for flight as a single unit. Detailed studies of different blended-wing body configurations for applies use as passenger aircraft have shown that, despite the disadvantages, additional bodies arranged in the airflow in the form of tail assemblies must be used to ensure rudder unit function. Without rudder units, there would be no adequate directional stability in flight, and in particular given the failure of an engine during takeoff.
Rudder units are required in aircraft with a blended-wing body configuration. It would here be possible to secure two rudder units to a central fuselage body in a non-central arrangement. On the other hand, it could also be possible integrate the rudder units into correspondingly dimensioned winglets. The rudder units are preferably arranged in mirror symmetry and spaced apart on an upper side of the aircraft.
Existing non-centrally arranged rudder units are given a neutral design in prior art. This means that, given the usual completely symmetrical profiling of the rudder units, all of their chords are tangential to the local inflow, and all local geometric angles of incidence on the rudder units equal zero. This yields exclusively one additional aerodynamic drag in the local profile plane and in the tail assembly, which increases the drag of the overall configuration and lowers the aerodynamic quality as reflected in the lift/drag ratio.
As a consequence, there may be a need for an aircraft or aircraft configuration with rudder units in a non-central arrangement, in which the aerodynamic quality and lift/drag ratio caused by the rudder units may be reduced to the lowest possible level. There may further be a need for modifying an already existing aircraft from prior art with rudder units in a non-central arrangement in such a way that their aerodynamic drag may be reduced without any greater outlay. In addition, other needs, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.